feat(pep): decide -> fulfill -> forward Decision Mode PEP (#2571)

[saurabhjain1592]

Ports the Decision Mode PEP (decide → fulfill → forward) contract into the Java SDK — the SDK analog of platform/shared/pep (ADR-056, epic #2563). Tracking: #2571.

Cross-SDK parity with the canonical Python (#211), Go (#181), and TypeScript (#241) PRs: JSON wire field names are byte-identical (snake_case), and constant VALUES match exactly (redact_pii, request/response, text/plain, allow/deny/needs_approval, paths /api/v1/decide, /api/v1/mcp/check-input, /api/v1/mcp/check-output).

What's added

• AxonFlow.decide(DecideRequest) (+ decideAsync) — the PDP step. POST /api/v1/decide over the SDK's existing HTTP Basic (org:license) auth; demo/wrong creds → AuthenticationException (401); a deny verdict is returned in the body (HTTP 200), not as an error.
• AxonFlow.fulfillRequest(DecideResponse, String) — discharges every request-phase redact_pii obligation by round-tripping the statement through the engine's check-input endpoint and returning engine-redacted content (FulfillResult: content + didRedact()). No local redaction anywhere.
• AxonFlow.decideAndFulfill(DecideRequest) (+ async) — the one-call path (DecideAndFulfillResult); fail-closed by construction.
• Pep constants + Pep.hasRequestRedaction(List<Obligation>).
• New types: DecideRequest (fluent builder), DecideResponse, Obligation, ObligationFulfillment, DecisionCallerIdentity, DecisionTarget.
• ObligationNotFulfillableException — the fail-closed signal (extends AxonFlowException).
• MCP types: content_type on MCPCheckInputRequest (+ content_type option on mcpCheckInput); redacted / redactedStatement / redactionEvaluated on MCPCheckInputResponse; redactionEvaluated on MCPCheckOutputResponse. Existing source-compat constructors preserved.

Fail-closed (never returns the original statement)

fulfillRequest throws ObligationNotFulfillableException when: no request-phase fulfillment; advertised content_types excludes text/plain; the endpoint is not the request-redaction path (foreign URLs rejected; absolute URLs accepted only when their path matches); the engine call fails / non-200; or redaction_evaluated == false. didRedact reflects whether the engine changed the content.

Verification

• Unit tests (34 new): decide parse + wire shape; every fail-closed branch (no-fulfillment, response-phase, unadvertised content-type, foreign endpoint, engine-error, redaction_evaluated=false, redaction_evaluated absent); passthrough (no obligation, engine-found-nothing); decideAndFulfill allow/deny/unfulfillable; hasRequestRedaction; absolute-URL acceptance. New-code line coverage 99.4%.

• Full suite: 1302 tests, 0 failures; JaCoCo BUNDLE gates satisfied (LINE 0.782, BRANCH 0.550).

• Wire-shape: validator green against the pinned community spec; baseline annotated for the acknowledged SDK-superset fields without bumping the pinned spec SHA (no spec-pin-bump needed).

• Version: minor bump 8.4.0 → 8.5.0 (pom.xml + example poms + CHANGELOG); Version Alignment script passes.

• runtime-e2e (runtime-e2e/decide_fulfill_obligation/, NO mocks): run against the live enterprise agent —

  decide -> verdict=allow decision_id=f8ed6956-... obligations=1 evaluated_policies=[sys_pii_credit_card, sys_pii_email]
  PASS step 1: decide returned allow + redact_pii request-phase obligation
  fulfillRequest -> didRedact=true content=Send the receipt to jo****************om and charge card 4**************1
  PASS step 2: fulfillRequest masked email + card via the engine (no local redaction)
  decideAndFulfill -> verdict=allow content=Send the receipt to jo****************om and charge card 4**************1
  PASS step 3: decideAndFulfill returned engine-masked content in one call
  PASS step 4: demo credentials refused -> AuthenticationException (HTTP 401)
  ALL PASS: decide -> fulfill -> forward verified through the SDK against the live agent
  

  Neither john.doe@example.com nor 4111111111111111 survives fulfillment.

Deviations from spec

• fulfillRequest returns a small FulfillResult (content + didRedact()) and decideAndFulfill returns DecideAndFulfillResult (verdict + content + decision) — idiomatic Java for the spec's multi-value returns; semantics are identical.

Refs #2563